1. Field of the Invention
Embodiments of the present invention relate to a method of forming a hybrid portable memory and a portable memory formed thereby.
2. Description of the Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
While a wide variety of packaging configurations are known, flash memory storage cards may in general be fabricated as system-in-a-package (SiP) or multichip modules (MCM), where a plurality of die are mounted on a substrate. The substrate may in general include a rigid base having a conductive layer etched on one or both sides. Electrical connections are formed between the die and the conductive layer(s), and the conductive layer(s) provide an electric lead structure for integration of the die into an electronic system. Once electrical connections between the die and substrate are made, the assembly is then typically encased in a mold compound to provide a protective package.
Flash memory modules may either be portable, as in the case of a land grid array (LGA) package, or dedicated, as in the case of a ball grid array (BGA) package. Portable flash memory modules are fabricated with contact fingers that allow the modules to be used as removable memory. They may be inserted into a slot in a host device, whereupon the contact fingers are brought into pressure contact with a printed circuit board in the host device to allow communication between the memory module and host device. Dedicated memory modules on the other hand are soldered, or otherwise permanently affixed to the printed circuit board of a host device.
Side and bottom views of a conventional LGA package 40 are shown in FIGS. 1 and 2, respectively. One or more memory die 20 and a controller die 22 are mounted on a substrate 24 in a stacked configuration, along with one or more passive components 26. Generally, the substrate 24 may be formed of a rigid core having thin film copper layer(s) on its top and/or bottom surfaces. An electrical lead pattern may be defined in the copper layer in a desired electrical lead pattern using known photolithography and etching processes. The copper film on the bottom surface may also be used to define a plurality of contact fingers 28 for communication with a host device. A plurality of test pads 30 are also defined in the copper film to allow electrical test and debug of the package. The test pads 30 are typically covered up once the electrical test is completed.
The die may be electrically connected to the substrate by wire bonds 34. Vias (not shown) are formed through the substrate to allow electrical connection of the die through the substrate to the contact fingers 28 and test pads 30. Once the die are electrically connected, the package may be encapsulated in a mold compound 38 (not shown in FIG. 1) to form the package 40. A typical package 40 is shown in a standard size SD lid 44 in prior art FIG. 3. Reduction in the size of the package 40 over time now allows the package 40 to take up only a fraction of the standard SD card lid.
A BGA package is formed in a similar fashion to the LGA package, but instead of contact fingers 28, a plurality of contact pads are formed on the bottom surface of the package. Once the package is fabricated, these contact pads receive solder balls, and the package may be mounted by the solder balls to a printed circuit board within a host device in a known reflow process.
In the above-described packages, the die are themselves packaged and include die bond pads formed in the upper surfaces of the die package. The die packages are electrically coupled to the substrate via wire bonds connected between the die bond pads and the substrate. An alternative mounting scheme includes leads which extend from the die package which are mounted directly to a substrate in a solder operation. Such mounting schemes are typically performed according to surface mount technology (SMT).
Instead of a substrate having a core and copper films, SMT die packages typically use a leadframe, which is a thin layer of metal on which one or more semiconductor die may be mounted. The leadframe includes electrical leads for communicating electrical signals from the one or more semiconductors to a printed circuit board (PCB) to which the leads are soldered. Common leadframe-based packages include plastic small outlined packages (PSOP), thin small outlined packages (TSOP), and shrink small outline packages (SSOP).
FIG. 4 shows a conventional SMT package 50. A leadframe-based memory die 52 and controller die 54 include leads 58 which are soldered to a PCB 56. Passive components 60 are also affixed to the PCB 58. Although not shown, contact fingers are formed on the back surface of PCB 56. Prior art FIG. 5 shows a typical SMT package 50 mounted within a standard size SD lid 44 (as in FIG. 3).
There is an ever-present drive to increase storage capacity within memory modules. One method of increasing storage capacity is to increase the number of memory die used within the package. In portable memory packages, the number of die which may be used is limited by the thickness of the package, which must not exceed a thickness of a standard-sized slot in the host device within which the memory module is received.